Chemistry Controls Dynamos in Metallic Cores: A Tour of the Solar System and Beyond

Joseph G. O'Rourke

Keynote Lecture Series


Joseph O'Rourke

Lecture Date and Time (US Mountain Time): 

Thursday, October 22, 2020 - 14:00

Lecture Link: 


Magnetic fields provide unique windows into the deep interiors of planetary bodies and their evolution over deep time. Most worlds in our Solar System with radii >1,500 km and metallic (iron-rich) cores are known to have a dynamo today or had one in the past. Simple models assume that dynamos typically arise from thermal convection, which leads to a simple criterion for dynamo activity: the total heat flow across the core/mantle boundary must exceed that which is conducted upwards along the adiabatic temperature gradient in the core. However, chemical processes in metallic cores, including crystallization of an inner core and reactions with the basal mantle, can overpower thermal convection. In this lecture, we will tour the galaxy to see how chemistry may help or hinder a dynamo. We will start on Earth and then travel to our Moon and the other terrestrial planets (Mercury, Venus, and Mars). Next, we voyage out to Jupiter to explore why one Galilean satellite (Ganymede) has an active dynamo but not the others (especially Io and Europa). Finally, we leave our Solar System to speculate about the significance of future detections of magnetic fields at super-Earth (or super-Venus?) exoplanets. Ultimately, the general importance of chemical processes to dynamos highlights the need to understand key material properties across a highly multi-dimensional space of pressure, temperature, and composition.

Speaker Bio: 

I am an Assistant Professor at Arizona State University in the School of Earth and Space Exploration, where I was previously an Exploration Postdoctoral Fellow. I received my PhD in Planetary Science from Caltech in 2017. I graduated from Yale University in 2012 with a BS in Astronomy & Physics and Geology & Geophysics.

My research is centered on understanding how processes deep within planets control their surface conditions (including atmospheric degassing, magnetic fields, volcanism, and tectonics). I’m potentially interested in any world made of ice, rock, and metal—so far including Earth, Venus, Mars, Titan, sundry protoplanets, and exoplanets of all sizes.

My primary tools are fundamental theory and numerical simulations, but I am increasingly involved in (and sometimes lead) mission and instrument proposals. I serve on the Steering Committee for NASA’s Venus EXploration and Analysis Group.

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